It is known in practice that wort kettles to which so-called vapor compressors can be connected are used when wort is being boiled for brewing processes. The vapor produced during boiling is introduced into the vapor compressor and the energy contained in the vapor is partly recovered. Vapor does here not escape to the outside. Vapor is introduced whenever the wort in the wort kettle has reached its boiling temperatures. Up to that time the vapor gradually forming during said process is passed to the outside through the vapor escape pipe. After the boiling temperature has been reached, a butterfly valve positioned thereon is closed so that the vapor is diverted towards the vapor compressor. When the vapor is being diverted via the vapor compressor, it must be ensured that neither excessive overpressure nor an excessive vacuum is created in the kettle in order to prevent damage to the kettle. It is therefore known that the pipe leading to the vapor compressor is operatively connected to a surge tank which has a pressure-regulating effect and, in case of excessive overpressure, diverts vapor via the vapor escape pipe and in case of an excessive vacuum sucks in air via the vapor escape pipe.
The disadvantage of said known construction must above all be seen in the fact that the shut-off devices designed as butterfly valves in the vapor escape pipes are relatively troublesome and expensive.